IMHO, the straight answer is that the 1:500k is perfectly OK for fixed wing flying, and the 1:250k offers additional detail which is relevant only if one is navigating using the map+stopwatch method.
The obvious drawback of the 1:250k is that you have quite a few of them, which becomes a hassle if going anywhere.
The Jepp 1:500k maps are poor in comparison with the UK CAA ones, and contain many ambiguities in airspace labelling (which is IMHO unacceptable) but are better than most other national maps, and practically speaking they are all there is for the majority of Europe.